Hamstrings

Musculi ischiocrurales

Also known as: hamstring muscles, ischiocrural muscles, posterior thigh muscles

The three posterior thigh muscles (biceps femoris long head, semitendinosus and semimembranosus) arising from the ischial tuberosity. They cross the hip and knee to extend the hip and flex the knee.

Overview

A true hamstring must (1) arise from the ischial tuberosity, (2) cross both the hip and the knee, and (3) be supplied by the tibial division of the sciatic nerve. By this definition the hamstrings are the long head of biceps femoris, semitendinosus and semimembranosus, together with the hamstring part of adductor magnus. The short head of biceps femoris arises from the femur, crosses only the knee, and is supplied by the common fibular division, so it is not a true hamstring.

The hamstrings extend the hip, especially when walking, when the trunk is held upright, and when rising from forward bending. They flex the knee. With the knee flexed, the medial pair (semitendinosus and semimembranosus) rotates the leg medially and biceps femoris rotates it laterally. In the late swing phase of running they decelerate the forward-swinging leg eccentrically, which is when most strains occur. Because they span two joints, hamstring tightness limits straight-leg raising and toe-touching (active insufficiency and passive tension).

Location

Posterior compartment of the thigh.

Parts & subdivisions

Biceps femoris

Lateral hamstring. Long head from the ischial tuberosity; short head from the linea aspera. Inserts on the fibular head.

Semitendinosus

Medial, superficial. Long tendon to the pes anserinus.

Semimembranosus

Medial, deep. Membranous origin. Inserts on the posteromedial tibial condyle.

Hamstring part of adductor magnus

From the ischial tuberosity to the adductor tubercle. Tibial nerve.

Anatomy

Origin

Ischial tuberosity (and the linea aspera for the short head of biceps).

Insertion

Head of the fibula (biceps), the superior medial tibia via the pes anserinus (semitendinosus), and the posteromedial tibial condyle (semimembranosus).

Action

Extension of the hip and flexion of the knee; rotation of the flexed knee.

Innervation

Sciatic nerve: tibial division (long head of biceps, semitendinosus, semimembranosus); common fibular division (short head of biceps).

Nerve roots

L5–S2

Arterial supply

Perforating branches of the profunda femoris artery; inferior gluteal artery (proximally); popliteal artery (distally).

Clinical significance

Hamstring strain

One of the commonest sports injuries, typically of the long head of biceps femoris during sprinting. Recurrence rates are high. Eccentric strengthening (Nordic hamstring exercise) reduces the risk.

Proximal hamstring avulsion

Forceful hip flexion with the knee extended (waterskiing, slipping into the splits) can avulse the common tendon from the ischial tuberosity. Significant retraction usually needs surgical repair. In adolescents the ischial apophysis can avulse instead.